Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$136.55	11.651%	$152.4594	$152.46	$152.45	$152.50
Purchase #2	$157.32	4.461%	$164.338	$164.34	$164.35	$164.30
Purchase #3	$8.94	3.690%	$9.2699	$9.27	$9.25	$9.30
Purchase #4	$164.35	7.422%	$176.5481	$176.55	$176.55	$176.50
Purchase #5	$80.90	13.457%	$91.7867	$91.79	$91.80	$91.80
Purchase #6	$21.54	11.611%	$24.041	$24.04	$24.05	$24.00
Purchase #7	$57.78	6.464%	$61.5149	$61.51	$61.50	$61.50
7 purchase totals =	$627.38		$679.9580	$679.96	$679.95	$679.90